<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8" />
		<title>demo</title>
	</head>
	<body>
		<script type="text/javascript" >
			function demo(){
				return setTimeout(() => {
					return 999
				}, 1000);
			}

			console.log(demo())
		</script>
	</body>
</html>